It is necessary to test substrates with electrical or electromechanical properties, such as semiconductor wafers, integrated circuits, multichip modules, printed circuit boards, flat displays and the like, during production. For this purpose, use is made of testing apparatuses which make contact with the substrates via probes. These probes are used to apply test signals to the substrates and/or for measuring a reaction of the substrate to the test signals.
In particular, such apparatuses are used for testing substrates in the field of semiconductor production. Here, the designation “prober” will be found. In this case, as a general rule, integrated semiconductor chips are tested in their assembly on a semiconductor wafer, as it is known. Wafers are composed of various materials, such as silicon, GaAs, InP or comparable materials and have a diameter of preferably 2″ to 12″ and a thickness to the order of magnitude of 90 to 500 μm. Following structuring to the wafers, the semiconductor chips produced in this way are tested and the semiconductor chips are then separated and subsequently finally mounted to form finished components.
In order to ensure the quality of the finished circuits, these have to be tested with suitable probers. The reactions measured in the process to the test signals supply information about the quality of each individual circuit by means of a comparison with the previously defined standards.
The testing in the wafer assembly, that is to say before the separation, is therefore advantageous since, following the separation, the individual chips would be difficult to handle for the testing, and testing could then expediently only be carried out following final mounting. However, this would mean that a not inconsiderable number of chips which do not meet the quality requirements would be finally mounted.
Typically, the semiconductor wafers are mounted and transported in wafer magazines. In this case, as a rule up to 25 semiconductor wafers are held with a vertical spacing from one another in the wafer magazine.
The sensitivity of the semiconductor wafers with regard to fracture and any kind of contamination forbids any contact with the human hand, for which reason handling robots are normally employed, which transport the semiconductor wafer from one processing station to another or transport it in or out of a wafer magazine.
Such a handling robot comprises a robot arm which is attached to a robot drive and, as a result, can be moved in a vertical degree of freedom (z) and two horizontal degrees of freedom (x, y) and can be pivoted about a vertical axis of rotation. Arranged on the free front side of the robot arm is a wafer holder which has holding arms which are provided with vacuum suction holders. These holding arms are able to grip the semiconductor wafer and move it in or out of a processing station or a wafer magazine, by the robot arm positioning its wafer holder directly under the underside or rear side of the semiconductor wafer by means of the robot drive and bringing it into contact. After that, the holding arms have a vacuum applied to them, so that the semiconductor wafer is held over the vacuum openings on the upper side of the wafer holder and can be transported from one position to another.
Probers of this type are employed in semiconductor factories, what are known as fabs, as production probers. In this case, these production probers take up a great deal of area, since a large number of such devices is provided. Because of the costs for the fabs, the areas taken up by the production probers are also very costly. Of these areas, large parts of the areas are provided for the production probers, in which engineers or operators can move in order to supply the automatic test systems continuously with semiconductor wafers to be tested.
Fully automatic test systems permit the operator or engineer to put in some wafer magazines and, with an initial setting made once, to operate until all the semiconductor wafers have been tested. A fully automatic test system of this type contains, in addition to the actual test arrangement, which substantially comprises a chuck, chuck driver, control electronics, probe or probe board and appropriate holding and connecting means, a pattern recognition system for wafer self-adjustment, CCD camera or microscope for observing the test substrate, monitor, handling system, wafer magazine station and alignment station.
It is, then, an object of the invention to reduce the space required and the costs which arise with the testing of substrates, in particular semiconductor wafers, during the production process.